Apparatus for tapping sheet metal



Nov. 21, 1939. J. H. PARSONS ET AL APPARATUS FOR TAPPING SHEET METALFiled Nov. 15, 1936 FIG.2.

INVENTORS JOHN H. PARSONS ROBERT M. POWELL Patented Nov. 21, 1939 UNITEDSTATES PATENT OFFICE APPARATUS FOR TAPPING SHEET METAL John H. Parsons,Pontiac, and Robert M; Powell, Detroit, Mich.

This invention relates to processes of and apparatus for tapping sheetmaterial, in a novel manner involving bodily distortion of the stock,and aims to provide, in such materials as sheet metal, a threadedopening so formed as to hold firmly a tap bolt, stud, or the like,regardless of the pitch of its thread, under conditions in which thelead of the screw exceeds the thickness of the metal. A further objectof the invention is the provision of means for automatically providingsuch opening with an edge bodily displaced to one side of the plane ofthe sheet, and lying upon an approximate helix, as well as provided withan edge bent to present one corner for engagement with the thread as thescrew enters, so that if necessary the pitch of the helix may bemodified by the bolt itself to correspond to the thread of the latter.

Another important object is the provision of improved combined punching,shearing, and forming means, adapted for use in conjunction with a punchpress of conventional construction, and arranged to punch, shear, andform the sheet metal in the manner described in a single operation.

A further object is the provision of such improved combined punching,shearing, and forming means so constructed as to form in sheet materialan opening having an edge of screwthreaded configuration and of noveland improved character, adapted to provide a better thread, calculatedto more firmly hold the screw, and so shaped as to give the helical edgeof the formed sheet metal a tendency to flow inwardly 35 and grip theshank of a screw when tightened into place, thereby providing a self-locking action strongly resistant to escape or loosening of the screw.

Other objects and advantages will'be apparent 40 from the followingdescription, wherein reference is made to the accompanying drawingillustrating a preferred embodiment of our invention and wherein similarreference numerals designate similar parts throughout the several views.In the drawing: Figures 1 and 2 show in perspective and in planrespectively a fragment of sheet metal provided with a helical-edgeopening formed by the apparatus, and in accordance with the. principles,disclosed herein.

Figure 3 is a perspective view of the male element.

Figure 4 is a perspective view of the female 55 element.

' (not, shown) Figure 5 is a side elevational view of the elements inoperative relation, showing the tool supporting means for the maleelement partly broken away and in section.

Figure 6 is a view similar to Figure 5, but upon 6 an enlarged scale, ofthe interacting parts of the elements, shown in the act of performingtheir work upon the sheet stock, the female element being partly brokenaway.

Figure 7 is a similar view of the parts in \the 10 act of performingtheir operation upon the work, taken at right angles to Figure 6, andsubstantially on the line 1-! thereof, looking in the direction of thearrows.

Figure 8 is a plan View of the female element. 1

Figure 9 is an end View of the male element.

Figure 10 is a perspective'view of a fragment of sheet stock providedwith the completed threaded opening, showing a screw inserted and heldtherein, but not locked in place.

Figure 11 is a fragmentary side elevational view of a male element ofsomewhat modified constructiom Referring now to the drawing, in whichFigures l and 2 illustrate the desired form of the finished threadedopening in the sheet metal, it will be seen that a central aperture H isprovided having a helical edge which, commencing substantially in theplane of the sheet and at one side of a radially shared line l2, risesuniformly about the circumference of the opening to its highest point atthe opposite side of the sheared line, thus providing lower and upperlips I3-l 4 for ready engagement with the thread of the entering screw.The metal joiningthe= upwardly projected helical edge to the hat body ofthe sheet is curved about a short radius, the

metal thus forming a conoidal rather than a conic section. In order topunch and form the metal in the manner described, we provide combinedpunching, shearing, and forming means the construction of which is bestshown in Figures 3 to 9 inclusive.

The members for performing the indicated operations comprise male andfemale'elements' irs 20--22 respectively, adapted to be supportedinaligned relation for movement into and out of operative engagement, asone by the ram and the other by the bed of a punch press or the like Forpurposes of description; it will be assumed that the male member is tobe mounted in the ram and the female element in the bed of the press.The male member, to the shank of whichis applied the general referencecharacter 20, carries a punching stem 25 projecting dow'nwardly from afiat land 30, and a shearing and forming blade 33 extends in inclinedposition from the periphery of the shank, at the land, to a point on thepunching stem spaced from its end. The shearing side of the angularblade comprises a flat surface which is extended longitudinally into theshank of the male member, as by cutting out the shank, in the mannerindicated at 35, to provide a continuous fiat surface from theangularcutting edge of the blade to a point well up the shank.

The female element is provided with a die opening 24 adapted to receivethe punching stem.

A depressed central area 26 surrounds the opening 24. Projecting intoabutting relation to the opening 24 is a substantially sector-shapedraised portion 28 having a flat, vertical, and radially disposed sidewall 3| forming a shearing edge and aligned with the side of blade 33which faces the opening 35. A slot 29 joins the depressed central areaand the exterior to form such cutting edge. Upon its other side, whichextends substantially tangentially to the die opening and is also formedby a .slot 32 joining the depressed central area with the periphery,.the edge of land 28 is curved downwardly, as indicated at 21, to allowthe downward bending of the metal necessary in the area surrounding theaperture H to impart the desired conoidal configuration.

Although the land 28 extends to a point adjacent the die opening 24, theremainder of the upstanding marginal portion 36 of the female member,surrounding the depressed area, is spaced outwardly from theopening,allowing the metal surrounding the punched-out central opening ll of thework to bend, downwardly in the desired curvature, the extent to whichit is bent being governed not merely by the shape of the male member,the angularity and thickness of the blade 33, but by the extent to whichthe male member is forced downwardly. By adjusting the travel of thepress ram, therefore, the extent to which the lip i4 is pressed out of,the plane of the remainder ofthe sheet, and so the pitch of the helix,may be varied, although it will be seen to be always necessary to presssuch lip entirely out of overlapping relation with respect to lip i3, inorder that a free edge may be presented to the entering screw.

Descent of the punch, after cutting out the central area, carries theweb 33 into engagement with the cutting edge 3| of land 28, to cut theradial sheared line. Due to the fact that the central depressed area ofthe die is substantially larger than the perforation, the work, exceptthat portion overlying the land 28, is supported only upon this circulararea spaced from the punch opening, allowing the metal to be carrieddownward and to bend naturally in a curved line. The area which formsthe lower lip is supported by the land 28, and so maintainedsubstantially in the plane of the sheet. The curvature at the pointdesignated 21 allows the gradual bending of the work from the low pointat lip I3, toward the remainder of the helix, from the fiat areaoverlying the land 28 to the section bent farthest out of plane bytheweb 33. I,

The functioning of the web 33 is best shown in Figures 6 and '7. Asthere indicated, after formation of the cut by its edge which bounds theopening 35, the opposite top corner of the Web presses downwardly uponthe metal at a point spaced from the line of shear, acting to bend the rmetal about a curved line, and by a multiplying action forcing theedgedownwardlyfarther than the blade extends, and imparting the desiredcurvature to the portion of the metal extending to the higher lip (thefrusto-conoid being formed in inverted position).

It is of course important that the elements be held in rigid alignmentand locked against rotation with respect to one another. For thispurpose the shank 20 is shown held in the ram of the press by means of aretainer mechanism corresponding to that disclosed in the copendingapplication of John H. Parsons et al., Serial No. 640,466, filed October31, 1932 (Patent No. 2,107,- 581, granted February 8, 1938). Theretainer comprises a block 40, apertured as at 4! to receive the shankand provided in its top face with a transverse channel 43 intersectingthe bore 4|, while a detent member 45 slidable in the transverse openinginto and out of the tool socket 4! is engageable with a slot as 4:? cutin the tool shank for locking engagement therewith. The detent member 45is actuable by a wedge cam 46 connected to an operating plunger 41projecting downwardly through the block and from the under side thereoffor convenient manipulation, a spring as 48 normally holding the wedgecam member in such position as to urge the detent into the tool socket,and so lock the tool in place, While when the plunger member 1'! ispressed upwardly and the wedge member released, the shank may easily beinserted and removed. The detent 45 extends transversely along a chord.of the cylindrical tool socket, and the slot in the tool shank similarlyextends transversely, whereby the detent holds the shank againstturning. The top of the slot in the tool shank will alsol be seen to beso inclined that urging of the detent inwardly by the spring 48 alsotends to force the shank into the tool socket.

Figure shows a screw inserted in the formed opening, and it will beapparent that, provided only the threads be stifi'er than the metal,fur-- ther tightening of the screw after its complete insertion to theextent there shown will result in drawing the raised portions and lip l4downward toward the plane of the sheet, flattening it against thebacking provided by the head of the screw given ram travel, the relativeproportion of the length of the sheared line to the distance the highcorner is thrown out ofplane. It will be seen that these factors may beaccurately controlled by varying the curvature of the blade in thisrespect.

While it will be apparent that the illustrated embodiments ofourinventionherein disclosed are well calculated to adequately fulfillthe objects .and advantages primarily stated, itis to be un.

by, and the shape of,

derstood that the invention is susceptible to variation, modificationand change within the spirit and scope of the subjoined claims. What weclaim is: 1. Means for punching, shearing and forming sheet material toimpart a desired configuration thereto, comprising cooperating male andfemale members, the former having a punch portionand a shearing blade ofsubstantial but definitely limited thickness intersecting and extendingoutward- N 1y from the punch portion, the female member having asubstantially flat work-backing rim,adie opening adapted to receive suchpunch portion and a countersunk area extending partly around the dieopening between such die opening and the rim, a substantially flat andsegmental land substantially co-planar with the rim of the female memberand extending inwardly to the die opening, said land having acooperating shearing edge positioned in operative alignment with oneface of the shearing blade, said rim having a circumferentialiyextending cut out area substantially wider than the thickness of theshearing blade, into and from which the blade is reciprocable, one sideof the cut out portion being defined by said shearing edge, wherebyexcess free bending of the work due to the thickness of the blade mayoccur in said cut out area without obstruction by the female member.

2. Means as set forth in claim 1 in which toward its outer extremitysaid shearing portion of the male member is inclined backwardly withrespect to the direction of projection of the punch portion.

3. Means as set forth in claim 1 in which the portion of the male memberoverlying said land is relieved to prevent engagement between the malemember and the work above the land.

4 Means as set forth in claim 1' in which the portion of the male memberoverlying said land is relieved to prevent engagement between the malemember and the work above the land, said male member also havingoutwardly extending portions overlapping the rim.

5. Means as set forth in claim 1 in which the male member extendsoutwardly and overlaps the rim.

6. Means as set forth in claim 1 in which the portion of the male memberoverlying said land is relieved to prevent engagement between the malemember and the work above the land, said male member also havingoutwardly extending portions overlapping the rim and substantially fiatand parallel to the rim.

7. Means as set forth in claim '1 in which toward its outer extremitysaid shearing portion of the male member is curved longitudinally andextends backwardly with respect to the direction of projection of thepunch portion.

JOHN H. PARSONS. ROBERT M. POWELL.

